(a) What are hormones?
(b) In a tabular form, state four differences between nervous coordination and hormonal coordination in humans.
(c) State three effects each of: (i) Over-secretion (ii) Under-secretion of thyroxin on mammals.
(d) Make a diagram 10 - 12cm long of the reflex arc and label fully.
(a) Hormones - These are chemical substances secreted by endocrine/ductless glands, directly into the blood/ circulatory system, which on reaching a target organ, stimulate activity of that organ.
| Hormonal | Nervous |
| Transmission is chemical | transmission is mechanical and chemical |
| slow transmission | Rapid transmission |
| Response is wide spread | Response localized |
| Target organs receive response | effector organs receive response |
| Long last response | short-lived response |
| pathway not specific through blood | pathway specific through nerves fibres |
(c)(i) Effects of over-secretion: -
(ii) Effects of under-secretion: -
(d) Labels: Receptor organ, sensory neurone, intermediate/relay neurone; motor neurone, synapse, spinal cord, ventral root, dorsal root, effector organ, spinal nerve.
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